In the production of thread or yarn, it has become the common practice to spin, twist or twine a strand consisting of one or more filaments or fibers more or less tightly in transferring it from a cop or bobbin to a yarn package or, more generally, from a strand-supply spool to a strand-takeup spool. One of the spool spindles is generally rotated about an axis to impart the desired twist to the strand while the other spool may merely be rotatable to take up or pay off the strand to be twisted.
When reference is made herein to a "strand," therefore, we intend to designate thusly any thread, yarn or other twistable and elongated member, consisting of one or more filaments or fibers and composed of natural or synthetic materials, which may be commonly subjected to twisting, twining a spinning in the aforedescribed manner. Further, we shall heretofore use the term "twisting" to describe the step of imparting a twist to a length of thread between a pair of spools, e.g. by rotating one of the spools and/or a thread guide or the like as is commonly known in the art. This term will therefore include the classical definition of spinning and twining. The twisting is usually accomplished between a pair of spaced apart contact locations, one on the twisting mechanism and the other at the nontwist-imparting spool. Also, reference to the spool "rotation" is intended to include rotation of the spindle, traveler-ring devices, etc. used to provide the contact location, whether or not the yarn body is actually rotated.
In most twisting devices, the strand-takeup spool and the strand-supply spool are mechanically connected together for joint operation so that he strand is wound upon the takeup spool at a given rate with respect to the twisting rate so that the strand is advanced at a definite feed rate (strand-feed rate) in units of length per unit time (e.g. meters per minute) while the twist-imparting spool is driven at another predetermined rate (twisting rate) generally given in terms of revolutions per minute or twists per minute. The number of twists per unit length (twists per meter) is then given as the quotient of the twisting rate and the strand-feed rate.
The ratio of the transmission means which operatively and positively connects the supply spool with the takeup spool thus is able to determine the number of twists imparted to the thread per unit length.
When a new thread length is to be added to the yarn package or for some other reason, a fresh length of the strand is to be knotted to a previously twisted length of strand in the space between the two spools, there remains an untwisted section as the two spools are again operated at their predetermined ratio of speeds. The knotted, formerly free end, of the previously twisted portion of the strand (e.g. on the yarn package or takeup spool) and the portion of the strand newly tied thereto, both are free from the twists which are normally imparted to the strand and hence the strand is not uniform. Spool processing may be carried out to impart an appropriate twist to this length and/or, the untwisting length may be ignored or removed after the yarn is otherwise finished. Poor quality thread is obtained or the processing costs are prohibitively increased.